-- chilling story that we'll have you wondering was it love. Or money it was an exotic honeymoon they came to a horrifying and a hundred feet beneath the ocean's waves. A scuba dive goes terribly wrong the newlywed bride lifeless on the ocean floor the groom. On the surface calling for help. Or guilty of murder here's ABC's Elizabeth Vargas for our series crime and punishment. This home video of a happy newlywed couple packing for their honeymoon in Australia is one of the last images of Tina Watson alive. Their fairy tale wedding behind them they set off to go diving in the Great Barrier Reef. She was very excited about her -- she was going to be the princess -- she wanted everything just perfect to had a plan perfectly. But eleven days later Tina was dead. Now Gabe Watson stands trial in an Alabama courtroom accused of murdering her. With Tina's parents front and center in their quest to find out what really how -- to their daughter. This is about -- just. Prosecutors began the trial this week by showing jurors this photo of Tina lying lifeless on the ocean floor. As shown in this Australian police reenactment video the prosecution believes Watson killed his new bride by turning off for air supply -- her scuba tank. And then holding her and a bear hug while she suffocated. They say he then turned the air -- on which is how what was found. All in under six minutes and the defense argues that scenario is impossible. And that -- and his death is a tragic accident. -- -- And -- her story culmination. Bad facts and bad circumstances. Until that point -- she was scared forward but it does wanted to go live now she's Brian. Today in court the jury watched a tape of Australian police questioning gave about the -- -- -- says -- struggle just women a strong currency and that she began to sink in the deep water. He says he signaled to her to inflate your buoyancy vest to help -- stay afloat but that she couldn't he then took her hand and tried to pull her -- long. Her hand and -- ask. Sideways. So. Had a radio. Gave then says he made a fateful decision to go up to the surface to get help for Tina in that split second decision that he made under water. -- 4550. Feet of water. When a current in -- face and his wife sinking away from them he made that decision to go for safety. And go for help up up up on the surface that decision he. Has been second guessed for nine years. Prosecutors say Gabe Watson has done more than second guess his actions that day they say he's changed his story about what happened several times. This -- he's changing his story. Well they -- he planned to kill his new life hearts and he could collect on her life insurance policy within minutes. -- -- -- But it wasn't -- who was the beneficiary of -- it was Tina's father Gabe Watson never received a dime. There had been tension between -- in Tina's family even before their wedding. They thought -- was cool and controlling of their daughter I don't paint that -- -- Tina's mother fraud that. This was the right guy for her since Tina's death those tensions have become an all out war between -- -- Tina's family. Tina's father fought to have Watson charged with murder in Australia. Gabe Watson did ultimately plead guilty to negligent manslaughter. Well the manslaughter standard that he pled guilty to -- a very obscure Australian law that says that if you undertaken dangerous activity with someone. You have a significant. Responsibility. To make sure that they're safe not that he killed there. But he didn't do enough to safer after spending eighteen months behind bars in Australia Watson returned home. Only to face murder charges again. States should. -- around. And acted in visual moment. Australian journalist in season diver Peter Patrick has been following the case for years. He says there is evidence -- story of what happened could be true that Tina could have panicked on this deep and difficult night. She shouldn't have been starving in the active for -- For a first -- -- for the very first time she'd been diving in -- and she -- -- what's really. -- -- significant. Diving event. -- and Tina were attempting what's called a drift dive over a century old shipwreck. Currents are so strong divers are told not to fight them but instead to drift over the submerged ship Patrick is -- on the dive himself. That wasn't a Formula One -- But. It -- would run around the rice -- where you need a lot of skills and you need to be but did she had just learned how to scuba in an Alabama pond. Where her instructors said she also suffered -- panic attack even in those calm waters. Divers use more air when they are fighting currents to swim or when they are packing. Tina's -- showed she had consumed an unusually high amount of air I think we -- it into the trial will body consistent with panic. And consistent with -- story. The -- organizers on the reef that date were found guilty of negligence and paid a fine for violating their own safety procedures. By letting a novice diver -- and escorted into the water. -- defense lawyers say that didn't seem to matter to police. They were so convinced of -- -- early on they turned what they saw as his unemotional response. Into evidence of -- When he returned to Alabama he met with grief counselors he attended a -- -- young widow and -- -- group a support group. Degree -- he -- he couldn't date. He couldn't. Interact socially. He was not -- and it took years. For him to heal and he still emotional. When he discusses. Two starkly different portraits of Gabe Watson are now on display. Stunned grieving widow -- Or calculating killer who left his new wife dying on the ocean floor. Twelve jurors will soon be asked to decide. I'm Elizabeth Vargas for Nightline in New York.

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